DeFi (or “decentralized finance”) is “an umbrella term for financial services on public blockchains.
With DeFi, one can do most of the things that banks support — earn interest, borrow, lend, buy insurance, trade derivatives, trade assets, and more — but it is faster and does not require paperwork or a third party.
As with cryptocurrency generally, DeFi is global, peer-to-peer (meaning directly between two people, and not routed through a centralised system), pseudonymous, and open to all.